For some time, glass encased, liquid temperature measuring devices were the only devices available for measuring temperature, including the temperatures of living things, with any accuracy. However, the use of such devices has always been fraught with potential danger. Glass tubes originally used for encasing the fluid were easily breakable. While alcohol is used as an indicating fluid under certain circumstances, mercury is the preferred fluid for easy and accurate measurement of human temperatures, but is a hazardous substance. In addition to the dangers posed generally to humans, such devices pose a particular potential danger to infants. Typically, the thermometer is anally inserted into the infant because of the much greater danger of breakage from oral insertion. However, infants often react to the insertion of a thermometer with vigorous movement, which may dislodge the thermometer or, more seriously, break the thermometer. Both the infant and the thermometer should be held during the entire temperaturemeasuring procedure, to prevent dislodgement, undue insertion or breakage of the thermometer.
Recent improvements in the area of clinical thermometer and temperature measuring devices have been in two major directions. One has been the development of electronic, probe-type thermometers. These represent a major improvement in safety and convenience. Commercially available electronic thermometers for home use typically include an exposed sensor tip at one end and an electronic display at an opposing, handle end. The devices are made of unbreakable plastic and metal materials and represent a significant increase in safety over glass thermometers. The temperature displays are typically digital and indicate a single number, making them both easier to read and to understand. Despite their improvements, such devices still must be continually held in order to prevent either dislodgement or injury to the infant. Also, the circuitry of such devices is typically designed to display an actual temperature when the actual temperature has been determined and not display another temperature until manually reset by the user.
Another direction of improvement in clinical thermometers has been toward the use of temperature sensitive liquid crystal devices. Certain materials, such as chlorestic esters, change physical states at predetermined temperatures or within a range of predetermined temperatures. Such crystals are discussed in great detail in U.S. Pat. No. 4,070,912 and 3,661,142. Use of such crystals in clinical thermometer devices is discussed in those patents, as well as in U.S. Pat. Nos. 4,509,533; 4,302,971; and 4,138,889. Related uses of such liquid crystals as body surface temperature diagnostic tools, particularly the formation of body clothing from liquid crystal fabrics, are disclosed and discussed in U.S. Pat. Nos. 4,524,778; 4,064,872; 4,043,324; 3,951,133; 3,847,139; and 3,380,224. U.S. Pat. No. 4,510,188; 4,048,359; and 3,852,092 discuss incorporating such materials into fabrics. U.S. Pat. No. 3,802,945 discussed the incorporation of such crystals into decorative novelty devices to be worn. U.S. Pat. No. 4,464,064 also teaches the use of such crystals as part of a room thermometer device.
Thermally responsive chemical temperature measuring devices have certain advantages and disadvantages when compared with mercury/glass and electronic thermometers. The primary advantages to the thermally responsive chemical devices are that they are essentially nonbreakable, contain no electrical or moving mechnical parts to wear or fail, and operate continuously as long as they are held against a patient, without the need to be reset. There are several disadvantages to these devices. They must have a separate, encapsulated chlorestic ester formulation for each discrete temperature indication. They are not designed for internal use. They are applied to a portion of the body, such as the face or chest, where they are visible in order to be read. Mostly, they are either adhered or simply placed upon the patient.
None of the aforesaid devices are optimally suited for continuous temperature sensing and temperature display from the preferred external body temperature measuring location, the armpit. Nor are any of the aforesaid devices particularly suited for the unattended temperature monitoring of infants.